D1X is a modification of the Descent 1 source that was released by
Parallax. It's mostly compatible with the Descent 1 v1.5, both in
multiplayer and on the local machine.
To play Descent1 you need to either need the full (registered/commercial)
version of the game and place the full version data-files in
/usr/share/d1x/full; or install the d1x-shareware package.